The function of some cyclin-dependent protein kinases (CDKs) has been remarkably conserved in evolution. Indeed, coding sequence for the human protein Cdc2 is able to substitute for the CDC28 gene in S. cerevisae and allow the yeast cell to grow and mate essentially normally. The following sequence near the NH2-end of the molecule is identical in both proteins: Gly-Glu-Gly-Thr-Tyr-Gly-Val-Val-Tyr -Lys-Ala. Does this mean that nucleotide sequences of the two genes coding for this region of the polypeptide are also identical

No, because the genetic code is redundant  

Explanation:

During the translation, a single amino acid may be coded for by more than one codon. It is for that reason that the genetic code is considered to be redundant. Tryptophan is the unique amino acid specified by a single codon. In this case, it is likely that silent mutations at the nucleotide sequence that encode for the Glu-Gly-Thr-Tyr-Gly-Val-Val-Tyr-Lys-Ala protein motif might have accumulated during the evolution of both CDK genes, modifying thus their nucleotide sequences while preserving the same protein sequence.

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added